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Power Calculator
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Conditions
Simple Vehicle Power Calculator
Calculator using Imperial Units
Vehicle Weight lbf
Vehicle Speed mph
You decide if laden, partially laden or unladen weight is used - the more heavily loaded the vehicle is the bigger the power consumption. Speed is that at which vehicle power is to be calculated, note that the faster the vehicle goes the more power it needs. HINT - if you are towing another wheeled vehicle/trailer/implement adding its weight here will bring it into the calculation (underlying assumption is that the Rolling Resistance specified below applies to both vehicle and trailer).
Rolling Resistance
Coefficient of rolling resistance, Cr
Rolling resistance is dependent on ground conditions and tyre/wheel design. Click here for help and suggestions on what value to use. The calculator assumes a single Cr for the vehicle (ie all wheels/tracks have the same Cr). Normally the Cr figure relates only to the natural resistance of a wheel to roll - ie issues such as bearing friction are not included. If you are likely not to use low friction bearings you might increase Cr to compensate. Alternatively specify a drive transmission efficiency below.
Gradient Climbing
Angle of climb, 1 in
Hill climbing can be a big contributor to required power - specify gradient in the form "1 in 10", "1 in 50", etc - anything flatter than 1:1000 will be taken by the calculator as on-the-level.
Aerodynamic Drag
Drag Coefficient, Cd
Vehicle Frontal Projected Area, in^2
or
Representative frontal width ins. Representative frontal height ins.
Air Density kg/m^3
Drag is strongly speed dependent and is felt much more at higher speeds than low. If you have a slow moving vehicle this component of drive force might be well be ignored.
Drag coefficient is dependent on vehicle shape. Click here for help and suggestions.
Either input the frontal projected area directly or specify the width and height of the vehicle (the area will then be approximated at 0.9 x W x H).
A value is suggested for air density at normal atmospheric pressure.
Vehicle Acceleration
NOTE - This is an input to the power calculation, not an output. It allows the calculator to determine the power required to achieve the specified acceleration - you state the required acceleration.
Change in speed mph
Time taken to achieve this speed change seconds
The calculator can work out the acceleration figure it needs if you tell it by how much vehicle speed changes over what period of time. For example 0 to 60 mph in 10 seconds can be specified as a 60 mph speed change in 10 seconds, or a 6 mph change in 1 second. 40 mph to 60 mph in 2 seconds can be specified as a 20 mph change in 2 seconds. The calculator assumes that this magnitude of acceleration is present at the vehicle speed specified at the top of the page.
Any Additional External Force
Ext Force lbf
This allows you to add in extra effects such as towing or pushing. If you have a tow bar pull you want to accommodate then you can add it in here.
Mechanical Transmission Efficiency
Effy %
The calculated power is the ideal mechanical power required at the wheels to drive the vehicle under the conditions you describe. The motor output power will need to be more than this - because some is lost in the mechanical transmission. If you specify a transmission efficiency (in %) a figure for motor output power will also be calculated.
A new window will open with a summary of your input data and the calculation results. Use the browser's "Back" button return to this page to run a repeat calculation with different input data. This way you can build up a picture of how the results vary with design and/or operating condition changes.
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